Apparatus and method for electrical precipitation

ABSTRACT

A liquid spraying electrical precipitator comprising a pair of electrically conductive walls and a plurality of spouts on each wall. A cleaning liquid such as water is applied to one of the walls, as by drippers at the top thereof, and flows downwardly to the spouts thereon. The liquid is caused to transit the gap between the walls by application of a strong electrical field. Preferably the wall of initial application is grounded, and the other wall is connected to a source of high positive potential. The electrical field so created causes negatively charged drops to be sprayed from the spouts on the first wall, and to follow a somewhat downwardly directed trajectory until they impinge upon the second wall. Water impinging on the second wall runs downwardly to spouts thereon, and is resprayed as positively charged drops across the gap to the first wall. This process is continually repeated until the water finally exits at the bottom of the precipitator. A stream of dirty gas flows upwardly through the precipitator, and is cleansed by the action of the positively and negatively charged drops continually spraying and respraying back and forth between the walls.

llnited States Patent Robertson Jan. 15, 1974 John A. Robertson,Chillicothe, Ohio [73] Assignee: The Mead Corporation, Dayton,

Ohio

[22] Filed: Mar. 22, 1972 [21] Appl. No.: 236,851

[75] Inventor:

Primary Examiner-Dennis E. Talbert, Jr.

Att0meyJohn W. Donahue [57] ABSTRACT A liquid spraying electricalprecipitator comprising a pair of electrically conductive walls and aplurality of spouts on each wall. A cleaning liquid such as water isapplied to one of the walls, as by drippers at the top thereof, andflows downwardly to the spouts thereon. The liquid is caused to transitthe gap between the walls by application of a strong electrical field.Preferably the wall of initial application is grounded, and the otherwall is connected to a source of high positive potential. The electricalfield so created causes negatively charged drops to be sprayed from thespouts on the first wall, and to follow a somewhat downwardly directedtrajectory until they impinge upon the second wall. Water impinging onthe second wall runs downwardly to spouts thereon, and is resprayed aspositively charged drops across the gap to the first wall. This processis continually repeated until the water finally exits at the bottom ofthe precipitator. A stream of dirty gas flows upwardly through theprecipitator, and is cleansed by the action of the positively andnegatively charged drops continually spraying and respraying back andforth between the walls.

10 Claims, 2 Drawing Figures APPARATUS AND METHOD FOR ELECTRICALPRECIPITATION BACKGROUND OF THE INVENTION This invention relates toelectrical precipitation of particles or droplets of contaminatingmatter from a flowing gas stream. More particularly it relates toprecipitators of the type wherein contaminated gas is caused to flowthrough a strong electrical field, and wherein the precipitating actionof the electrical field is aided by water particles. Examples of such aprior art device are disclosed in Marks U. S. Pat. No. 3,503,704 andWintermute U. S. Pat. No. 2,245,516. Most commonly, however, prior artprecipitators are characterized by either electrical field precipitationor charged particle precipitation, but not both. For instance, Darrah U.S. Pat. No. 1,958,406 and Romell U. S. Pat. No. 3,440,799 disclosedevices employing charged liquid particles for precipitation of gasparticulates, but the gas does not flow through a strong electricalfield. Alternatively, there are dry electrostatic precipitators such asthose disclosed in Hahn U. S. Pat. No. 1,980,521, Thompson U. S. Pat.No. 1,992,974 and Shively et al. U. S. Pat. No. 2,195,431 whereinparticulate matter is precipitated by an electrostatic field, butwithout any charged liquid particles in the precipitation region.

A common problem with dry electrostatic precipitators has been theaccumulation of precipitated matter on the collection electrodes. Thishas necessitated periodic shutdown for flushing. In some devices,however, the accumulation problem has been solved by arrangementswhereby the collection electrode is grounded and continuously flushed bya cleansing liquid. A typical example of continuous flushing of thecollection electrode is shown in DeSeversky U. S. Pat. No..

3,238,702. Wintermute U. S. Pat. No. 1,959,752 discloses continuousflushing of discharge electrodes. It will be appreciated that in suchliquid flushing systems, the flushing liquid cleans only the electrodesand not the contaminated gas.

SUMMARY OF THE INVENTION This invention provides for simultaneousprecipitation of gas contaminates by an electrical field and by liquidparticles in a compact, efflcient, and mutually compatible manner. Theliquid particles are introduced directly into the electrical field andtransit continually back and forth across the field for efficientutilization of cleansing liquid and continuous cleansing of the fieldcreating electrodes.

The apparatus for practicing this invention comprises a pair of parallelelectrode surfaces and a plurality of liquid collecting spouts on eachsurface. The two electrodes are oppositely charged to set up anelectrical field therebetween, and a flow of cleansing liquid issupplied to at least one of the electrode surfaces. The liquid thensprays continually back and forth between the electrodes by collectionupon the spouts and electrical attraction therefrom. Concomitantly ionsof pposite electrical polarity are generated at the two sets of spoutsand cooperate with the electrical field and the criss-crossing waterspray to produce a novel combined cleansing action.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat schematicvertical crossection of a precipitator made in accordance with thisinvention.

FIG. 2 is an exploded view of a portion of one electrode plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment ofaprecipitator built in accordance with this invention is shown in FIG. 1.As illustrated therein a contaminated gas enters precipitator 1 throughan inlet pipe 4 and exits through a discharge port 7. During its passagethrough precipitator l the gas passes between a pair of walls 2 and 3equipped with spouts l3 and 14 respectively. Walls 2 and 3 are similarin construction, and preferably contain a large number of spoutsarranged in rows as shown more particularly in FIG. 2.

An electrically conductive cleansing liquid such as water is admitted toprecipitator 1 via an inlet pipe 5 for distribution by manifold 8. Thewater leaves manifold 8 by means of a row of small tubes 21 attachedthereto and trickles down to spouts 13. The water flow rate throughtubes 21 may be adjusted by adjustment of the fluid level withinmanifold 8, or alternatively, by filling manifold 8 completely andadjusting the inlet flow rate at pipe 5.

The water reaching the first row of spouts l3 flows downwardly to thetips thereof, and is pulled therefrom by a strong electrical field. Thisfield is created by grounding wall 2 as by line 10 and raising thesurface of wall 3 to a high positive potential as by line 11. Thiscauses the water on spouts 13 to become negatively charged and to besprayed across the inter-electrode space to wall 3. The negativelycharged water particles scrub the flowing gas during this transit.

After reaching the surface of wall 3, the water flows downwardly tospouts 14. Upon reaching the tips of spouts 14, the water is sprayedback to the surface of wall 2 as positively charged droplets. Uponreaching wall 2, the water gives up its positive charge, flows down wall2 to the next row of spouts l3, and flows downwardly therealong forrespraying to the surface of wall 3. The process continues with thewater traversing a downwardly directed zigzag path characterized bypositively charged sprays l5 and negatively charged sprays 16. It isapparent that the flowing gas is continually scrubbed by the alternatesprays, and that the continued reuse of the cleansing water results in agreat water economy. The waste water, with contaminating matterentrained therein, eventually flows into waste collection trough 9, andleaves precipitator 1 via waste outlet pipe 6.

It will be appreciated that the electric field concentration at thespout tips not only sprays water as above described, but also causesionization of the passing gas. Ions of both positive and negativepolarity are created; positive ions in the vicinity of spouts l4 andnegative ions in the vicinity of spouts 13. Thus the contaminated gas iscleaned by both scrubbing and precipitation.

The charged wall 3 is electrically isolated from ground by means ofinsulators l2. Deflector plates l7, l8, l9, and 20 are provided toprevent migration of water particles to the region behind wall 3.Precipitator l is preferably closed out at the ends thereof by dieIectric walls, not shown.

As shown more particularly in FIG. 2, wall 2 comprises a backing board22 and a conductive faceplate 23. Backing board 22 may be made of anyconvenient conductive or nonconductive material, but the correspondingbacking board in wall 3 preferably should be nonconductive. Plate 23 maybe an aluminum plate of about 25 mils thickness and must be inelectrical communication with ground line 10. Spouts l3 (and likewisespouts 14) may be made by a simple metal stamping and bending process,and preferably should be bent upwardly about 60 from apertures 24. Thespouts thus make an angle of about 30 from the horizontal, and functioneffectively with a wall spacing of about 2 inches and a potential ofabout +20,000 volts on wall 3. It has been found that the precipitatoroperates most effectively with a large number of spouts arranged in rowsas illustrated. One particularly effective configuration has a spout rowspacing of about 3 inches and a center-to-center spacing of aboutthree-sixteenths inch between spouts in a row. In this configuration thespouts are about three thirty-seconds inch wide at their base and areabout inch long. The gas flow rate ideally should be about to 12 feetper second. The arrangement may be made as wide as desired toaccommodate any gas flow requirement. Parallel plate operation is alsopossible. Furthermore, any desired collection efficiency may be obtainedby serial cleansing in a stack of such precipitators.

It has been observed that proper adjustment of the water flow rate hasan important bearing on the efficiency of precipitators made inaccordance with this invention. In particular for a unit built as abovedescribed with electrode walls 36 inches high by 36 inches wide, a flowrate of about 150 cc per minute has been found to be about optimum. Thepreferred mode of operating such a unit is to adjust the water flow to aproper rate and then gradually raise the operating voltage on wall 3until electrical arcing is observed. Thereafter the voltage is reducedto a level just below arcing and the system is ready for operation. Asstated above the usual operating voltage is about +20,000 volts. Thisprecipitator has been found to be very efficient at removingcontaminating matter from gas streams, and has been unexpectedlyeffective in removing small particles having a diameter of 1 micron orless.

It is apparent that spouts 13 and 14 need not be arranged in spaced rowsas described above, but this arrangement is preferred because it allowsfor placement of a large number of spouts in a small area with littleinterference between positively charged sprays 15 and negatively chargedsprays 16. Avoidance of such interference is desirable so as to preventcollisions between positively and negatively charged water particleswith concomitant loss of momentum and charge. Particles which do collidehave a tendency to coalesce and fall directly downward into the flowinggas stream.

There is another preference to be observed in the arrangement of spoutsin spaced rows. That is that there be one or more rows of spouts 14 at alevel lower than the lower row of spouts 13. This eliminates the needfor a waste trough below wall 3.

Instead of the spout configuration shown in FIG. 2, one may employ anyother configuration adapted to collect water and carry it to a point ofhigh electrical field strength. Also, tubes 21 may be replaced by anyother means adapted to distribute a film of cleansing liquid along theupper surface of plate 23. In another embodiment cleansing liquid may besupplied to a dripper device and dripped upon deflector plate 17.

What is claimed is:

1. Apparatus for cleansing a contaminated gas comprising:

1. a first wall member provided with an electrically conductive surface,

2. a second wall member mounted in substantially parallel relation tosaid first wall member and provided with an electrically conductivesurface facing the conductive surface of the first wall member,

3. a first series of protuberances mounted on the first wall member andextending toward the second wall member,

4. a second series of protuberances mounted on the second wall memberand extending toward the first wall member,

5. means for supplying a gas cleansing liquid to at least some of theprotuberances in said first series,

6. means for causing said contaminated gas to flow through the spacebetween said wall members, and

7. means for establishing an electrical field between said wall memberswhereby said cleansing fluid is induced to spray back and forth betweensaid conductive surfaces and said protuberances and concomitantly cleanthe flowing gas.

2. Apparatus according to claim 1, said first and second wall membersbeing upstanding, said protuberances being downwardly directed spouts,and said means for supplying a gas cleansing liquid comprising means forflowing said liquid downwardly over the conductive surface of said firstwall member to be collected by the spouts mounted thereon and sprayed asaforesaid.

3. Apparatus according to claim 2, the conductive surfaces of said wallmembers being of planar configuration.

4. Apparatus according to claim 3, said spouts being arranged in spacedhorizontal rows, the rows of spouts on said second wall member beingvertically displaced relative to the rows of spouts on said first wallmember 5. Apparatus according to claim 3, further comprising means tocatch and carry off used cleansing fluid and a pair of dielectric endwalls closing out the ends of said first and second wall members.

6. Apparatus according to claim 2, said means for causing gas flow beingoperative to produce flow in an upward direction.

7. Apparatus according to claim 2, said means for establishing anelectric field comprising a D.C. voltage source connected to theconductive surface on said second wall member and means for groundingthe conductive surface on said first wall member.

8. Apparatus according to claim 7, said D.C. voltage source being ofadjustable positive potential relative to ground.

9. Method of cleansing a contaminated gas comprising the steps of:

l. passing said gas between a pair of substantially parallel electrodesurfaces each provided with a series of projections extending inwardtoward the other plate,

2. supplying an electrically conductive cleansing liquid to theprojections on at least one of said plates,

3. establishing an electrical field between said electrodes, and

10. Method according to claim 9, the strength of said electrical fieldbeing adjusted to a magnitude just slightly below that at whichelectrical arcing commences.

2. Apparatus according to claim 1, said first and second wall membersbeing upstanding, said protuberances being downwardly directed spouts,and said means for supplying a gas cleansing liquid comprising means forflowing said liquid downwardly over the conductive surface of said firstwall member to be collected by the spouts mounted thereon and sprayed asaforesaid.
 2. a second wall member mounted in substantially parallelrelation to said first wall member and provided with an electricallyconductive surface facing the conductive surface of the first wallmember,
 2. supplying an electrically conductive cleansing liquid to theprojections on at least one of said plates,
 3. establishing anelectrical field between said electrodes, and
 3. a first series ofprotuberances mounted on the first wall member and extending toward thesecond wall member,
 3. Apparatus according to claim 2, the conductivesurfaces of said wall members being of planar configuration. 4.Apparatus according to claim 3, said spouts being arranged in spacedhorizontal rows, the rows of spouts on said second wall member beingvertically displaced relative to the rows of spouts on said first wallmember.
 4. a second series of protuberances mounted on the second wallmember and extending toward the first wall member,
 4. adjusting thestrength of said field to a magnitude great enough for production ofcontinuous liquid spraying back and forth between said electrodes butlow enough to avoid substantial arcing between the electrodes.
 5. meansfor supplying a gas cleansing liquid to at least some of theprotuberances in said first series,
 5. Apparatus according to claim 3,further comprising means to catch and carry off used cleansing fluid anda pair of dielectric end walls closing out the ends of said first andsecond wall members.
 6. means for causing said contaminated gas to flowthrough the space between said wall members, and
 6. Apparatus accordingto claim 2, said means for causing gas flow being operative to produceflow in an upward direction.
 7. Apparatus according to claim 2, saidmeans for establishing an electric field comprising a D.C. voltagesource connected to the conductive surface on said second wall memberand means for grounding the conductive surface on said first wallmember.
 7. means for establishing an electrical field between said wallmembers whereby said cleansing fluid is induced to spray back and forthbetween said conductive surfaces and said protuberances andconcomitantly clean the flowing gas.
 8. Apparatus according to claim 7,said D.C. voltage source being of adjustable positive potential relativeto ground.
 9. Method of cleansing a contaminated gas comprising thesteps of:
 10. Method according to claim 9, the strength of saidelectrical field being adjusted to a magnitude just slightly below thatat which electrical arcing commences.